Good question. Here’s what I found:

The phrase “you’re a shoe in” is actually correctly spelled as “you’re a shoo-in”. The term “shoo-in” first appears in print in 1928. It originates from the horse racing industry, where it describes a horse that’s a guaranteed winner in a rigged competition. The term comes from the word “shoo,” which means to urge something in a direction. In this context, a “shoo-in” is someone who is very likely to succeed.

“Mind your Ps and Qs”

The phrase “mind your Ps and Qs” means to be on one’s best behavior or to mind one’s manners. The origins of this phrase are disputed and several theories have been proposed:

Teaching children: Some language experts believe it comes from teaching children how to distinguish lowercase p and q.
Pints and Quarts: Another explanation suggests it is an abbreviation for “mind your pints and quarts” in British pubs.
Pleases and Thank-yous: A third theory claims it is short for “pleases” and “thank-yous”.
1602 play by Thomas Dekker: Some believe it comes from a 1602 play by Thomas Dekker.

The first print sighting of the phrase dates to 1756. However, the true origin of the phrase remains unknown. It’s fascinating how phrases can have such varied and interesting histories!

(I love sayings)

https://www.phrases.org.uk/meanings/phrases-and-sayings-list.html

Merriam-Websters (11th ed.) says the term originated in 1937.

What can I say…

The Oxford Dictionary states that the term “shoo-in” first appears in print in 1928.

guess it depends on which dictionary you put more stock in

HA! There’s another saying…“put stock in”. too funny”

“Shoo-in” was originated in the early 1920’s during the era of horse racing meaning skating over the finish line. How skate turned into shoo I’ve never found other than it was normal human interaction where one person said it, another liked it & it spreads through family & friends & it became regular use.

Now, “shoe-in” grew out of the era of the door-to-door salesmen around the 1950’s & 60’s where the d-2-d salesmen would slide their shoe in between the door & the door jam so the housewife couldn’t slam the door & wouldn’t move it until she bought something from him which gave him a guaranteed sell of his product.

Both references means basically the same although they have different yet somewhat similar origins.

Mind your Ps and Qs could also come from the movable print industry, where those letters (identical in shape but opposite in orientation) would be individually placed into the printing plates.

Good thinking @RocketGuy !